Transformer oil composition



Patented Dec. 17, 1940 UNITED STATES 2,225,533 TRANSFORMER OIL COltflOSITION Milton A. Dewey, Wilmington, Del.,

assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application July 26,1938, Serial No. 221,424

9 Claims.

This invention relates to transformer oil compositions highly resistant to undesirable oxidational changes, and comprising petroleum oils containing in admixture therewith relatively small amounts of a combination of addition agents exceptionally useful in protecting said oils against oxidation and sludge formation.

Petroleum oils are widely used in electrical transformers, primarily for the purpose of dissipating heat from the windings to the transformer case, and also for the secondary purpose of electrical insulation. Such oils must possess sufficiently low viscosity tofacilitate transfer of heat by convection, low pour point to prevent solidification of the.oll at low temperatures, high flash and the points to reduce danger of explosion and fire, low volatility in order to minimize evaporation losses, highdielectric strength, and resistance to oxidation, and must be of such character as to emulsify with water only with the greatest diiilculty.

. Petroleum oils used for this purpose ordinarily comprise distillate oils refined to such extent as to possess the characteristics noted above to as great an extent as is possible. oils do undergo oxidational changes which result in the formation of insoluble matter or sludge. This is in turn undesirable not only because of the fact that sludge so formed tends to render the oil more susceptible to form emulsions in the presence of condensed water, but because a the deposition of sludge on the windings of the transformer tends to reduce the efliciency of heat transfer. These oxidational changes, while slow, are nevertheless serious because of the fact that transformer oils are ordinarily employed over exceedingly long periods of time. Oxidation of the oil tends to be'promoted bycontact of the oil with metals (especially copper), varnishes and insulating materials, by catalysis or otherwise.

In determining the value of oils for use in transformers, some sort of accelerated oxidation test is ordinarily employed. One commonly used method of testing comprises subjecting the oil to contact with air or oxygen at moderately elevated temperatures in the presence of copper or other metal tending toincrease the oxidation of the oil. The results of such tests are commonly evaluated both in terms of the so-called induction period, that is to say, the time which elapses prior to. the appearance of sludge in the oil when subiected to the test, and in terms of the amount of sludge formed per day after the first appearance of sludge. The ultimate consideration must, of course, be the However, these combined effect of these two factors, which may conveniently be expressed as the time which elapses between the start of the test and the development of a fixed quantity, say 0.1 per cent, of sludge in the oil.

There are a num r of substances which, when 5 added to petroleum oils, tend to increase the induction period of the oil as measured by a test of the character indicated above, and there are other substances which tend to decrease the rate of sludge formation after theinitial appearance n ofsludge. Since both factors are important and must be considered in order to determine the ultimate value of the compounded oil, there is need for a combination of agents which when added to petroleum oil will yield a compounded 16 oil or composition having both a high induction period and a low rate-of sludge formation per day; that is to say, an oil in which the length of time required to form a given amount of sludge, under accelerated conditions of oxidation, 2

will be high.

Unfortunately, however, antioxidants of various types are not ordinarily cumulative in effect and the eifect of a combination of antioxidants of various types cannot be predicted from con- 25 sideration of the effects of the individual agents when these agents are added alone to petroleum oils. v

I have found, however, that petroleum oils to which have been added relatively small amounts 30 of diphenylamine and certain alkylated phenols possess exceptional utility as transformer oils and that when these agents are used in combination, the effect of the combinationis from an over-all standpoint considerably better than could have been predicted from the behavior of the individual agents, when added alone. The total effect is not merely cumulative or additive.

Both of these types ofcompounds are of some value individually as antioxidants but combinatlons thereof are unpredictably eflicient.

- The alkylated phenols contemplated by my invention are alkylation products of phenols and substituted phenols, in which there are present alkylation linkages of secondary or preferably tertiary type. They do not include phenol itself or such alkyl substituted phenols as the cresols, iwlenols and ethyl phenols themselves but they do include tertiary butyl, tertiary amyl and sim 5o ilar alkyl derivatives of such phenols, as well as similar'derivatives of benzyl-substituted, cyclohexyl-su stituted and other substituted phenols. The preferred members of the class contemplated are those in which at least one or both of the g tertiary or secondary alkyl ness, is 2,6-di-tertiai-wbutyl--methyl phenol. 0ther alkylated phenols which I have found useful include the following:

2,6-di-tertiary-butyl-4-ethyl-phenol 2,6-di-tertiary-butyl-i-cyclohexyl-pheno1 2,6-di-tertiary-butyl-4-benzyl-phenol 2,4,6-trl-tertiary-butyl-phenol 2,6-di-tertiary-amyli-methyl-phenol For .the most part, such alkylated phenols are readily prepared by alkylating phenols or substituted phenols with olefins, such as isobutylene, under conditions favorable to promote alkylation, as for example under heat lprzsence of the usual acid condensing agents, or

pounds so prepared. I In general, the amounts of such materials employed more than 0.5 per cent 'of di-phenylamine in any case. Similarly the amount of alkylated phenol employed is ordinarily somewhat larger than the amount of dlphenylamine employed. I have used 0.3 per cent and 0.2 per cent by weight of the nary specifications for transformer oil. Acid-refinedand solvent-refined oils may be employed, and in some instances it is desirable to employ oils which have been subjected both to acid-refining and solvent-refining methods.

The following data will further serve to illustrate the application of my invention and utility thereof:

These test data were obtained in accordance with the sludge formation test for mineral transformer oil, described by F. M. Snyder intheir paper entitled Testing for sludge formation in mineral transformer oil presented at the thirty-ninth annual meeting for the American Society for Testing Materials. The technical investigation described in the aforesaid paper was carried out in collaboration with the laboratories of a considerable number of firms engaged in oil refining and in the manufacture of electrical equipment.

Briefly, samples of oil are maintained in tubes containing copper wire at a constant temperature of approximately 120 C. The tubes are open at the top to an enclosedair space and dry air is passed at a controlled rate of 1 to 2 cubic feet per hour through the enclosed space above Into each tube is introduced or oil composition to be tested, a

Clark and E. A.

days as compared with 5.5

groups is or are in a number of tubes intervals the tubes are successively removed and the amount of sludge determined. The results of per cent of sludge.

The oil employed in all of the tests set forth a typical petroleum transformer oil, commonly used for the purpose indicated. The results obtained in testing the oil alone and in testing the oil together with both the individual addition agents and combinations thereof are as follows:

TABLE I Rate of gs gmdse digit. 10D onus-- Run I Sample tested pgdod' on Deb g g sludge A Oil base without addition 0 0. 0114 8.5

agen

B Same oil plus 0.3% of 2,6-dil0 0. 0250 14 terlitiary-butyl-d-methyl pheno O Samefloil plus 0.1% diphenyl- 1 0. 0110 10 D Sane oil plus 0.3% of 2,6-di- 9.5 0.0080 23 tertiary-butyl-i-methyl phepol plus 0.1% diphenylamme.

' E Same oil plus 0.3% of 2,6-di- 8 0.0270 11.5

terltlary butyl-i-ethyl-pheno F Same oil lus 0.3% of 2,6-di- 8 0.0055 26 tertiaryutyl-4-ethyl phe- :10] plus 0.1% diphenylam- G Same oil plus 0.3% of 2,6-di- 2 0.0110 11 tefitiaiiy-butyli-cyclohexyl- H Same oil plus'0.1% of 2,6-di- 2 0.0058 19.5

tertiary-butyl-4-cyclohexyl- 511113301 plus 0.1% diphenyl- I Same oil plus 0.37 of 2,6-di- 2 1.0100 13 terltiary butyl-diienzyl-pheno J Same oil plus 0.3% of 2,6-di- 2 0.0030 34 tertiary butyl-d-benzyl-phepol plus 0.1% diphenylamme.

It will be evident from the above that the combination of addition agents in accordance with my invention is far more eil'ective, in terms of over-all effectiveness, than any of the individual agents considered alone. Thus, comparing the runsA,B,CandD,itwillbe phenylamine, on the other hand, increased the rate of sludge formation thereafter to a very slight extent only, thereby increasing the total days to form 0.1 per cent of sludge by only 1.5 days.

Whereas the alkylated phenol, as in run B,

mation of sludge, the combination of these two materials results in a very striking decreasein the rate of sludge formation, namely down to 0.0080 Consequently, the combination of the two addition agents, as shown in run D, increases the total days to from 0.1 per cent of sludge from 8.5 to 23 days, an increase of 14.5 days and 1.5 days for being employed. At prescribed aaassfaa addition agents when employed alone. These results clearly indicate that these the individual far more effective when employed with each other than when emthat the oil compositions of my invention are also effective in reducing the deterioration of transformer insulating tape. The results given in the following table are-typical of these tests.

,TABI-III Eflect of transformer oils on insulating tape,

95 hit, 200 F.

Geinin till?! 1 n percent Color of Oil oil, N. P. A.

Transformer oil alone Same transformer oil plus 0.3% 012 o-di -butyl+mothyl-phenoi plus 0.1% phenylamine It will be obvious tothose skilled in the art that my invention is not limited to the specific examples given hereinabove by way of illustration and exempliflcation, but may be variously practiced and embodied within the claims hereinafter made.

What I claim is:

l. A transformer oil comprising a petroleum oil, normally subject to oxidational deterioration resulting in the formation of sludge, having in admixture therewith relatively small amounts of diphenylamine and a secondary or tertiary alkyl phenol, the amounts of said last-mentioned agents present being sufficient at least to substantially retard sludge formation.

2. A transformer oil comprising a petroleum oil, normally subject to oxidational deterioration resulting in the formation of sludge, having in admixture therewith relatively small amounts of diphenylamine and a secondary or tertiary alkyl- 50 substituted cresol, the amounts of said last-mentioned agents present being suillclent at least to substantially retard sludge formation.

-3. Atransformer oil comprising a petroleum oil, normally subject to oxidational deterioration resulting in the formation of sludge, having, in admixture therewith relatively small amounts of diphe'nylamlne' and a secondary or tertiary alkylsubstitut'ed and bensyl-substituted phenol, the

similar oil composiscope of the being sumcient at sludge formation- I 4. A transformer oil comprising a petroleum oil, normally subject to oxidational deterioration resulting in the formation of sludge, havlng in admixture therewith relatively small amounts of diphenylamine and a substituted and cyclohexyl-substituted phenol, the amounts of said last-mentioned agents present being suflicient at least to substantially retard sludge formations H 5. A transformer oil comprising a petroleum oil, normally subject to oxldational deterioration resulting in the formation of sludge, having in admixture therewith relatively small amounts of diphenylamine and a secondary or tertiary alkylsubstituted phenol, wherein at least one of the secondary or tertiary allrvl groups occupies a position ortho to the hydroxy group, the amounts of said last-mentioned agents present being sufncient at least to substantially retard sludge formation.

6. A transformer oil comprising'a petroleum oil, normally subject to oxidational deterioration resulting in the formation of sludge, having in admixture therewith relatively small amounts of diphenylamlne and 2,6-dl-tertiary-butyl-4- methyl phenol, the amounts of said last-mentioned agents present being suflicient at least to substantially retard sludge formation.

7-. A transformer oil comprising a petroleum oil, normally subject to oxidational deterioration resulting in the formation of sludge, having in admixture therewith relatively small amounts of diphenylamine and 2,6-di-tertiary-butyl-4-cyclohexyl phenol, the amounts of said last-mentioned agents present stantially retard sludge formation.

8. A transformer oil comprising a petroleum oil, normally subject to oxidational deterioration resulting 'in the formation of sludge, having in least to substantially retard admixture therewith relatively small amounts of" diphenylamine and 2,6-di-tertiary-butyl-4-benzyl phenol, the agents present being suflicient at least tosubamounts of said last-mentioned stantially retard sludge formation.

9. A transformer oil comprising a petroleum oil, normally subject to oxidational deterioration resulting in the formation admixture therewith about 0.3 per cent of 26-111- tertiary-butyl-4-methyl phenol and about 0.1 per cent of diphenylamine, said last-mentioned agents being effective in combination both to retard the appearance of oxldational'sludge in the oil and the rate of sludge formation thereafter.

MILTON A. DEWEY.

of sludge, having in amounts of said last-mentioned agents present secondary or tertiary alkylbeing suillcient at least to sub- 

